This application claims the benefit of a Japanese Patent Application No. 2001-189566 filed Jun. 22, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to input or output (hereinafter simply referred to as input/output) control apparatuses, input/output control methods and information storage system, and more particularly to an input/output control apparatus and an input/output control method which control input and output from a host unit to a plurality of slave units, and to an information storage system which employs such an input/output control apparatus or an input/output control method.
There are information storage systems which manage data using a disk unit such as a hard disk drive. In some information storage systems, a RAID structure is used to protect the data from a damage to the disk drive. According to the RAID structure, a plurality of disk drives are provided, and a redundant structure is employed so that the original data can be restored even when a portion of the data is destroyed.
Input and output requests from a main frame system may be directed to different disk drives. In such a case, an input/output control apparatus is provided between the main frame system and the information storage system, so that the input and output can be made efficiently and the plurality of disk drives can be accessed simultaneously.
A request which needs to be executed with priority exists within the input/output requests from the main frame system. For this reason, a mechanism is provided to execute the request which needs to be executed with priority over other input/output requests.
2. Description of the Related Art
In the information storage system, the input/output requests are queued in an input/output queue, and are thereafter distributed to device queues of the requested devices.
FIG. 1 is a diagram for explaining an example of a conventional queue. In FIG. 1, input/output requests from a host unit 1 are queued in a cache queue 2 in a requested order. The requests queued in the cache queue 2 are queued in device queues 3a and 3b of corresponding disk drives 4a and 4b in the requested order, and the requests are executed in the corresponding disk drives 4a and 4b. In this state, in the device queues 3a and 3b, the queuing order of the requests to the device queues 3a and 3b are changed based on the priority order of the corresponding requests. As a result, the requests with the higher priorities are executed with priority over other requests having lower priorities.
However, in the conventional information storage system, the requests from the host unit 1 are distributed to the device queues 3a and 3b via the cache queue 2. Hence, if the disk drive 4a is the request destination of a highest priority request of the cache queue 2 but the device queue 3a of the disk drive 4a has no vacancy, the queuing must wait even if there is vacancy in the device queue 3b of the disk drive 4b which is the request destination of a next request of the cache queue 2. Consequently, there were problems in that the request is delayed, and that a response time cannot be guaranteed.
Accordingly, it is a general object of the present invention to provide a novel and useful input/output control apparatus, input/output control method and information storage system, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an input/output control apparatus, an input/output control method and an information storage system, which can transfer data efficiently with devices.
Still another object of the present invention is to provide an input/output control apparatus for controlling input/output requests from a host unit to a plurality of subordinate units, comprising a priority order managing section which controls a priority order of the input/output requests based on priority orders of the input/output requests given by the host unit, for each of the subordinate units. According to the input/output control apparatus of the present invention, it is possible to reduce the waiting time of the input/output request having a high priority order in the queue, and to guarantee a response time of the input/output request having the high priority order, because the order of the input/output requests in the queue is changed depending on the priority order.
A further object of the present invention is to provide an input/output control method for controlling input/output requests from a host unit to a plurality of subordinate units, comprising the step of (a) controlling a priority order of the input/output requests based on priority orders of the input/output requests given by the host unit, for each of the subordinate units. According to the input/output control method of the present invention, it is possible to reduce the waiting time of the input/output request having a high priority order in the queue, and to guarantee a response time of the input/output request having the high priority order, because the order of the input/output requests in the queue is changed depending on the priority order.
Another object of the present invention is to provide an information storage system for controlling input/output requests from a host unit to a plurality of subordinate units, comprising a priority order managing section which controls a priority order of the input/output requests based on priority orders of the input/output requests given by the host unit, for each of the subordinate units. According to the information storage system of the present invention, it is possible to reduce the waiting time of the input/output request having a high priority order in the queue, and to guarantee a response time of the input/output request having the high priority order, because the order of the input/output requests in the queue is changed depending on the priority order.
Two requests having identical priority order may be queued so that a latter received one of the two requests is queued to a lowest priority position. In this case, it is possible to reduce the wait time of the input/output request having a low priority order, and to prevent a considerable delay in a response time of the input/output request having the low priority order.
The priority order managing section may include a first managing section which manages the priority orders of the input/output requests from the host unit, for each of the subordinate units, and a second managing section which manages input/output with respect to the subordinate units. In this case, it is possible to reduce the wait time of the input/output requests by changing the order of the input/output requests in the queues managed by the first and second managing section depending on the priority order.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.